Heat treatment of high aluminumiron alloys



atent Ofiice Patented Oct. 24, 1961 3,005,738 HEAT TREATMENT OF HIGH ALUMINUM- IRON ALLOYS Dusan Pavlovic, Forest Hills, and Karl Foster, Pittsburgh, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania No Drawing. Filed Aug. 16, 1957, Ser. No. 678,539 6 Claims. (Cl. 148120) This invention relates to aluminum-iron alloys and in particular it concerns the production of high aluminumiron alloys characterized by outstanding magnetic properties in the resulting products.

It is a primary object of the present invention to pro vide a method for heat treating high aluminum-iron alloys to develop superior magnetic properties in the resulting product.

It is another object of this invention to provide magnetic aluminum-iron alloys outstandingly characterized in one or more of the magnetic properties.

An additional object is to provide improved methods for rolling brittle aluminum-iron alloys to thin gauges.

It is another object to provide methods according to the foregoing objects that can be practiced with existing equipment and skills and does not require particular training for their successful utilization.

Aluminum-iron alloys containing about 16 percent aluminum have heretofore been annealed in a protective atmosphere, such as hydrogen, at a temperature of 900 C. to 1050 C. However, it has been reported that the magnetic properties of the resulting material were substantially independent of the temperature of treatment.

In contrast to the reported results of other investigators we have discovered that, surprisingly, at least one magnetic property, and generally two or more, of magnetic aluminum-iron alloys containing at least 14 weight percent of aluminum and annealed in a protective atmosphere such, for example, as dry hydrogen, can be significantly affected when a sufi'lciently high temperature is used. As a consequence of this discovery we have been able to pro duce aluminum-iron alloys that have superior magnetic properties of coercive force (H in oersteds), remanence (Br in gauss) and maximum permeability (u as compared with those properties of aluminum-iron alloys treated according to procedures known heretofore.

In practicing our invention, a magnetic aluminum-iron alloy containing at least 14 percent aluminum is heated in a protective atmosphere, eg. helium, hydrogen or the like, at a temperature sufficient to bring about atomic disordering of the aluminum-iron being treated. The phrase disordering has heretofore been used by others to indicate the change that occurs in these alloys at a temperature on the order of 530 to 550 C. whereby the atomic structure changes from ordered F e Al to an ordered FeAl type lattice, or the reverse depending on whether the temperature is being raised or lowered from that point. When that temperature is referred to in this specification, it will be denominated as the ordering transformation temperature. By disordering we mean to indicate a change in atomic structure from an ordered structure to a disordered or random structure. The exact temperature of disordering depends on the specific composition involved, but in general we have found that temperatures on the order of at least 1100 C. and preferably l150 to 1300 C. should be used to bring about that result effectively. The ameal suitably extends for at least about 15 minutes and generally for 1 to 5 hours or more. We now believe that the lL'gh annealing temperature and the resulting disordering of the atomic structure are largely responsible for the observed improvement in magnetic properties.

The treatment applied to the alloy at the termination of the annealing step is determined by the magnetic property that is to be developed and the composition of the alloy being treated. By Way of example, if outstanding values of coercive force and maximum permeability are to be developed and the alloy being treated is a magnetic aluminum-iron containing at least 15.2 weight percent of aluminum,the alloy most suitably is furnace cooled, i.e. cooled at a rate of about to 150 C. per hour, to a temperature approaching, but not as low as, the ordering transformation temperature. At that point, the alloy is quenched to room temperature. The resulting product has a very low coercive force and a greatly improved maximum permeability. Quenching is initiated from above the temperature at which the structure normally would change from FeAl to Fe Al. That temperature is a characteristic of each specific composition, but for the alloys of this invention it generally occurs at about 530 to 5 50 C. We have actually used temperatures of about 550 C. for quenching and have obtained very satisfactory results. However, to be sure that a sufliciently high temperature is used, we prefer toinitiate quenching from a temperature of about 600 to 750 C. Higher temperatures can, of course, be used but no particular advantage in magnetic properties is obtained at higher temperatures while there is an increased chance of destroying the material due to thermal shock, as by cracking the alloy, since a greater temperature range is involved. Quenching may be accomplished in any manner desired, and such fluids as water, brine or oil may be used as the quenching medium.

Another variation of the invention concerning the alloy treatment after the annealing step involves obtaining products with the surprisingly low remanence values of less than 2000 gausses and even less than 1000 gausses, in a certain range of compositions, combined with a low coercive force. For this embodiment, the alloys are treated in the manner just described for the production of products with a low coercive force and a high maximum permeability. However, the alloy compositions that are useful contain from about 14.0 to about 15.1 weight percent aluminum broadly. In this embodiment we have been able to produce strips and tapes 5 to 10 mils thick of alloys that have a composition of about 14.6 to 14.9 weight percent aluminum and the remainder iron with a remanence value of below -0 gausses and a coercive force of at least as low as 0.15 oersted at an induction of 12000 gausses. As will be shown hereinafter, a relatively low remanence can be obtained in the higher aluminumirons, but a long soaking period is required to secure that result.

In preparing the products mentioned so far, we have found it desirable to hold the alloy at or about the temperature from which quenching is to be initiated for a time sufficient to insure that a. substantial thermal equilibrium in the structure has resulted. Generally about 5 to 15 or 20 minutes is satisfactory for this purpose. This step, however, constitutes another possible variable in the general process. In studying this variable we made the additional discovery, upon which this embodiment of the invention is predicated, that apparently a kinetic condition exists with respect to at least some of these alloys and that it can be expected that there is an optimum correlation between the time each alloy of specified composition is held at the quenching temperature and the actual quenching temperature used. Making use of that additional discovery we have been able to produce alloy strips and tapes of 5 to 10 mils thickness with a maximum permeability as high as 90,000 gausses and the low coercive force of at least as low as 0.020 oersted at an induction of 7000 gausses by holding an annealed 16.6 to 17.0 percent aluminum-iron at a temperature of about 700 C. for a period of time of about 50 to 70 minutes, and then quenching from that temperature. Holding the alloy at that temperature for shorter, i.e. about minutes, or longer, i.e. 8 or so hours, periods of time results in a markedly lower value of maximum permeability. Hence, for this particular composition, a holding time of about one hour is critical with respect to having an outstanding combination of high maximum permeability and low coercive force. a

The materials to which our invention applies are magnetic aluminum-iron alloys containing aluminum in amounts of at least 14 percent by weight. Aluminumiron alloys are non-magnetic at an aluminum content that is greater than about 17.5 weight percent. Therefore, the broad range of compositions of the alloys that can be treated in accordance with our discoveries can be stated to be aluminum-iron alloys containing 14 to 17.5

weight percent of aluminum it being understood that the upper limit is to be construed to include all the alloys which are magnetic at about room temperature and is not an absolute va'lucJ Other alloying constituents and incidental impurities may be present in varying amounts provided they do not deleteriously interfere with obtaining the improved properties in the resulting products.

The alloys for the present invention can be prepared by any procedure desired. One procedure that we have used with satisfaction involves melting, in a vacuum furnace, a pure iron, such as electrolytic iron, and commerically pure aluminum suitably having a purity on the order of 99.99 percent. The aluminum is melted under a blanket of helium, or other inert gas, to prevent loss. The melt may be cast in a vacuum or under a protective atmosphere to prevent the uncontrolled introduction of impurities. The ingot is then rolled to the desired thickness.

In preparing sheet or tapes for use in the present invention we have used thicknesses of about 3 to 25 mils because most commercial application utilize materials having a thickness within that range, though it should be understood the invention can be practiced with strips of other thicknesses. The alloys with which this invention is concerned are very definitely brittle alloys. Accordingly, the ingots must be reduced to the final thickness with great care, if the losses of materials in that operation are not to make the process prohibitively expensive. Any successful rolling schedule known may be used such, for example, as that recently reported and known in the art as the warm rolling method. That procedure requires fairly rigid control of the rolling temperatures, which are restricted to but slight deviation from 575 C. to produce the structure needed for the subsequent cold rolling that is done to obtain thin gauge material.

The alloy ingots or plates preferably are reduced to the desired thickness by use of our discoveries concerning methods of rolling these brittle alloys. We have discovered that these brittle aluminum-iron alloys can be rolled to very thin gauges without the necessity. of using extremely close temperature control or specially constructed strip-annealing furnaces. This result is achieved by hot rolling the alloy, in air or hydrogen, or other atmosphere, taking a (reduction in each pass within the critical limits of 10'to 15 percent regardless of the'thickness of the material being rolleddown to the cold rolling gauges of 7 to 14 mil thicknesses. Hot rolling by definition indicates rolling at any temperature above the recrystallization temperature, and we generally roll at about 1000" C. In that manner we have been able to produce thin gauge material that also has a structurepermitting cold rolling, readily. More important, however, by this discovery we avoid having to use the tedious and expensive warm rolling procedure, above mentioned and heretofore thought essential to obtain a structurecapaole of being cold rolled, to obtain thicknesses of suitable structure for cold rolling. After hot rolling, the resulting product can easily be cold rolled to the ultra-thin gauges 4 of the order of 0.001 inch and even thinner with any desired reduction per pass, using intermediate anneals between reductions when necessary. Those anneals need extend but a few minutes and normally are conducted at 700 to 1100 C. a

Successful cold rolling of these brittle alloys had heretofore been said to be dependent upon preparative rolling in a manner that develops a fibered microstructure in the material. Warm rolling accomplishes that result. A part of the explanation of the ability to hot roll these alloys in the manner just described, i.e. above the recrystallization temperature, can be attributed to the increased ductility of the alloy at the higher temperature involved. We have discovered an additional method of rolling that takes advantage of both of these ideas. In this embodiment we melt the alloy to include a small but effective amount of zirconium or similar metal, such as titanium, sufiicient to result in an alloy having a higher recrystallization temperature than does the same alloy free from the added metal. Under those circumstances the alloy can be rolled below the recrystallization temperature, thereby producing the fibered structure and avoiding the complicating factor of recrystallization. However, rolling is done, under these conditions, at a temperature above the warm rolling temperature heretofore mentioned and the advantage of the increased ductility at the ltu'gher temperature is obtained. For example, 16 percent aluminumiron has a recrystallization temperature of about 600 to 650 0., depending on the percent reduction and time at the annealing temperature. On the other hand, the ternary alloy of 16 percent A1, 0.1 percent Zr and the remainder iron has a recrystallization temperature of about 850 C. Accordingly, the ternary alloy can be Warm rolled at temperatures as high as 850 C. and result in the desirable elongated microstructure characteristic of a cold rolled product much more easily than when rolling the binary alloy. In this embodiment it is evident that a wider temperature range than the range for the prior warm rolling procedure may be used and the process is, therefore, considerably easier to control and to practice, particularly in commercial operations. Moreover, the magnetic properties of the ternary alloy compare very favorably with those of the binary alloys, whereas the rolling characteristics, and consequently the rolling econornics, are definitely improved by the presence of zirconium. For these purposes we generally use about 0.05 to 0.5 weight percent of zirconium or other ternary constituent but other quantities may be used if the apparent change in cost and properties make it desirable.

Another way of improving the rollability of high aluminum-iron alloys is to increase the inherent ductility of these alloys at room temperature. This effect can be obtained by the addition of elements such as boron and silicon in small amounts, suitable up to about 0.5 percent of boron or up to about one percent of silicon, as a supplement for aluminum.

EXAMPLE I Several alloys were prepared by the following procedure: electrolytic flake iron was melted in a magnesium oxide crucible in an induction heated vacuum furnace at a pressure of 0.1 micron. Helium was then admitted to the furnace and aluminum was added in predetermined amounts to produce alloys with aluminum contents of 15.6, 16.0 and 16.2 weight percent. The resulting melts were cast in steel slab molds. When the ingots had solidified, they were hot-rolled at 1000" C. with reduction held within the range of 10 to 15 percent per pass to 0.007 inch sheets. a

Two sets of ring laminations were stamped from each sheet. One set of each composition was heat treated in Table I Alloy Heat Run percent Treat, H, Br u Al "O From these data it is apparent that materials produced in accordance with our invention are characterized by a much lower coercive force and a markedly higher maximum permeability than are those made according to known procedures. Comparing l and 2 it can be seen that use of our invention results in a coercive force that is only 66 percent of that obtained at a 900 C. heat treatment, and the maximum permeability increased by more than 40 percent. Even better results were achieved with the 16.2 percent alloy since the coercive force was about 75 percent less or only about 55 percent of that obtained at 900 C., and the maximum permeability was over 65 percent higher. Consequently for such applications as magnetic amplifiers and transformer cores, the materials of our invention will result in considerably improved efiiciencies.

Similar results may be obtained where a ternary alloy is produced as shown in the following example.

EXAMPLE II Ternary alloys having the compositions indicated in Table II, were prepared in substantially the same manner as described above in Example I. The ingots were rolled at 1000 C. to a thickness of 0.125 inch. These eighth inch plates were then reduced to sheets 0.007 inch thick by warm rolling at a temperature maintained between 600 and 700 C. After the final rolling pass, the sheets were annealed for 15 minutes at 650 C. Two sets of ring laminations were stamped from each of the resulting sheets, with one set being heat treated at 900 C. in dry hydrogen for two hours while the other set was'heated at 1200 C. in dry hydrogen for two hours. was then furnace cooled to 600 C., held for 15 minutes and then water quenched. The data on the properties of the products are as follows:

Table II Heat Run Alloy 1 'ILrsa; He Br um;

900 .110 3,800 19,300 7 1,200 .031 2, 900 sagoo 900 .020 3,100 19. }155% 200 .028 3.000 7 03 1 Remainder iron.

Here again the pattern of results evidenced in the data in Table I appear. Marked improvement in the values of coercive force and permeability result when the 1200 C. anneal is used. Considered as a percentage change, it is evident that the presence of zirconium and boron are Each set a Comparing these data with those in Table III, it may particularly eflective. The silicon-containing alloy, as expected, behaved essentially in the manner as would a binary alloy containing 16 percent aluminum, the one percent of silicon simply performing as an additional one percent of aluminum. The room temperature ductility and consequently the rollability of these ternary alloys is considerably improved over the corresponding binary aluminum-iron. Ductility was determined by an Erichsen test on the 0.007 inch sheets. The boron addition was found to be especially efiective for this purpose.

EXAMPLE III A comparison also was made of the results obtained by heat treating at 1000 C. as compared with heat treating in accordance with this invention, all other steps and conditions in the process being the same. The data obtained in this test are as follows:

From these data it can be seen that properties of a 15.9 percent aluminum-iron alloy treated at 1000" C. (No. 3, Table I) are similar to those of a 16 percent alloy treated at the lower temperature of 900 C. (No. 13). It can be noted however, that upon raising the treating temperature (compare 3 and 13) the values of coercive force and maximum permeability were somewhat degraded and definitely not improved. Accordingly, it could be expected that a further rise in temperature would degrade the product even further. Surprisingly, no such degradation occurred, but to the contrary the coercive force and maximum permeability were greatly improved (compare 14 with 3 or 13).

EXAMPLE IV Table IV Run Heai great, H. Br um be seen that the improved results secured as a consequence of our discovery are essentially independent of the initial quenching temperature provided, of course, that the quenching temperature used is at least as high as the transformation temperature (550 C.). In other words, a marked improvement in magnetic properties results whether a low or a high temperature is used at the initiation of the quenching step.

The foregoing examples amply demonstrate our broad discovery that temperature has a surprisingly favorable ,efiect on the magnetic properties of high aluminum-iron alloys. The following examples serve to point out the manner in which optimum values of particular magnetic properties can be developed.

EXAMPLE V Two alloys for this investigation were melted in a vacuum fumace, using electrolytic iron and 99.9 percent aluminum shot as raw materials and following the general proceduredescribed in Example I. The ingots produced were hot rolled at 1000 C. to a thickness of 0.007 inch. Ring laminations were punched from the rolled sheets in the usual manner for heat treatment and magnetic testing. a

All heat treatments were done in an atmosphere of dry hydrogen in a tube furnace. At the times when the furnace was open to allow the insertion or removal. of a charge, a helium atmosphere was used. After the heat treatments the specimens were furnace cooled to the quenching temperature and then quenched in water. The specimens were sandwiched between Inconel plates to prevent excessive mechanical shock during quenching.

Three representative heat treatments were used on the 14.7 percent aluminum-ironalloy while the 15.0 percent alloy was treated with only the best heat treatment; they are listed below in Table V. The data obtained are as follows: i V V Table V Heat Run Treat 1 Ho Br O.Quench") (3) Heat 2 hours at 1200 0.; furnace cool to 600 0.; hold for 1(5 111061;

utcs at 600 0.; quench in Water to room temperature. C.Quench) .Runs 19 and 20 are of particular interest because of the exceptionally low remanence of the products. The comparison of all the runs show that, within these particular composition ranges, a' quenching treatment, rather than slow cooling, and a high temperature (1200 C.) anneal, rather than an intermediate temperature anneal, are essential. to the production of products with this unusual combination low remanence, high permeability and low coercive force. These materials may be used in meters, current transformers, relays and pulse transformers. e

We have made further studies of these materials to see if we could improve the remanence even more than as shown above.

a An aluminum-iron containing 14.8 weight percent of aluminum was prepared'by the procedure hereinbefore described. Three sets of ring laminations of the alloy were heat treated at 1200 C. for 2 hours in dry hydro.- gen. One set was then furnace cooled 575? C held forminutes and then water quenched A second set *was cooled'to 610 C., held 15 minutes and water quenched, While the third set was cooled at 700 (3., held for one hour and then water quenched. The remanence value for the second and third sets was 940 gausses. The remanence value for the first set, however, was the low value of 490 gausses. These data show the reproducibility of the results. They also show that at compositions of about 14.8 percent aluminum, there is no particular advantage in holding the alloy at quenching temperature for extended periods. On the other hand by more closely approaching-the ordering transformation temperature, the best values of remanence were obtained.

- In still further studies in the preparation of materials with low remanence, we deterrninedthat as the aluminum content increases, long soaking periods at the quenching temperature are necessary to obtain remanence values of below 2000 gausses. For example, a 15.3 weight percent aluminum-iron heated in dry hydrogen for 2 hours at 1200 C. and held at the quenching temperature of 700 C. for 9 hours prior to water quenching had a remameme of only 1,718 gausses. 16.8 percent alloy heated in dry hydrogen at 1200 C. for two hours andthen held 'at the quenching temperature of700. C. for four hours EXAMPLE VI Electrolytic flake iron was annealed in wet and then in dry hydrogen for decarburization and dcoxidation,

respectively. It was then melted in an induction heated magnesium oxide crucible in a vacuum-pressure furnace. Helium was admitted to the chamber and commercially pure aluminum was added to the molten iron. The melt, in a 15 to 20 pound batch, was cast in a slab mold mounted on a copper stool. The ingot obtained was rolled to a 0.007 inch thick sheet. Ring laminations 1 /2 to 2 /2" O.D..were punched from the sheet. Sets of these laminations were annealed in dry hydrogen (dew point -.6() C. or better), furnace cooled to quenching temperature, held at the quenching temperature for a measured time and then water quenched to about room temperature. The alloy contained 16.8 weight percent of aluminum and the remainder iron. The data obtained on the resulting products and the heat treatment used in each instance are shown inthe following table.

Table I Run Heat Treatment Ho B; Bn= um 21 900 C1 hour. 610 0% 0.026 2,287 8,470 38, 960

hour; W.Q. from 610 O.

22..." 900 C.=Lhour,700 0. 4 0.026 2, 400 6,500 49,400

hour; W.Q. from 700 C. I

23 900 C.4 hours, 15 min. 0.0245 2,409 8,900 54, 800

at 600 0.; W.Q. from 600 C.

24..-" 1100 05-4 hours, 1 hour 0.019 2, 630 6, 700 90, 530

at 700 0.; W.Q. from 700 0.

25 900 G.-2 hours, 4 hours 0. 030 2, 870 6, 500 45, 830

at 700 0.; W.Q. from 700 0.

26-.- l200 C.2 hours, 9 hours 0.082 1, 375 10, 200 9, 233

at 700 0.; W.Q.f rom 700 C. t

2 7... OO.-2hours,Fun1aee 0.236 2, 875 10,200 5, 570

cooled to room remperature.

28 1300 O.2h0ur5, Furnace 0.715 4, 085 10, 100 2, 600

cooled to room temperature; 8 hours at 450 0., Furnace cooled to room temperature.

29.--- v1200 O.2 hours, M11011! 0.029 3, 540 8. 2 80 58, 570

at 600 0.: W.Q. from 600 0.

W.Q'. indicates water quenching.

From the data under the heat treatment column it will be noted that runs 21,22, 23, 25, 27 and 28 are outside the limits of this invention because they either were annealed at a low temperature or they were furnace cooled to room temperaturerather than being quenched. These data are included to further demonstrate the criticality of the factors involved in this invention. From the runs wherein the processing involved 900 C. anneals, it can be noted that neither the quenching temperature nor the time at quenching temperature significantly affected the coercive force or the permeability of the product. nealing at a higher temperature and then cooling to room temperature without quenching seriously degraded the products as is shown in runs 27 and 28. The data shown in runs 24, 26 and 29 are within the scope of this invention. Run 26 shows the low remanence of the alloy when held at quenching temperature for very extended periods.

.Run 24, shows the combination of very high maximum 9 an hour. Upon comparing runs 26 and 29 with run 24 the critical eifect of holding time on these two properties may be seen.

A similar series of tests was conducted on alloys of other compositions, e.g. the 16 percent alloy. Time at soaking temperature had no particular effect and did not produce a result comparable to that shown in Example Vi. This further demonstrates the unexpected nature of the results in this series of tests.

The alloys useful in this invention are magnetic aluminum-iron alloys containing 14 to 17.5 weight percent of aluminum. Impurities are, of course, present in all these alloys. A typical analysis of the impurity content of an aluminum-iron containing 14.7 weight percent of aluminum (soluble) is, in weight percent, as follows: 0.05 percent insoluble aluminum, 0.006 percent carbon, 0.01 percent silicon, 0.007 percent phosphorus, 0.002 percent sulfur and 0.001 percent manganese. We have presented a large quantity of test data on most of the alloys and have accumulated far more but have not included it in view of its redundant nature. However, this large number of tests made on alloys of each composition have randomized such diverse influences as an impurity, thereby lending conclusiveness to the results shown as being produced by proceeding in accordance with our discoveries.

It should also be noted that the alloys reported herein were all 0.007 inch thick. This, too, was done to insure soundness of the conclusions drawn from the data, it being well known, for example, that thickness has an eflect on magnetic properties as shown by the data in the following table:

1 Conditions of these runs were essentially identical to limit the variables to be only the thickness.

2 15.8% Al-Fe; Ring Laminations. Accordingly, data on alloys of different thicknesses would not be strictly comparable. However, alloys of thicknesses other than 7 mils can, of course, be treated in the manner described, and we have actually done so, with comparable results being obtained.

From the foregoing, it is readily apparent that this invention provides a method whereby aluminum-iron materials of outstanding magnetic properties are obtained. This discovery has been made notwithstanding the teachings of published art indicating to the artisan that it would be of no avail to heat treat aluminum-iron alloys at very high temperatures. Contrary to those indications, we have found that with the defined alloy group, the temperature of annealing can have a very significant eilect on the resulting products. Moreover, we have discovered that particular compositions within the bro-ad range studied can be treated to optirnize a particular magnetic property. Hence, by coupling our annealing treatment with a controlled application of one or more of the other variables, outstanding speciality products can be produced. The resulting magnetic materials may be substituted for the commercially available silicon-iron and nickel-iron alloys that are now used in magnetic applications, with an advantage of cost, space factor, and ethciency in addition to a great advantage in mechanical properties.

According to the provisions of the patent statutes, we have explained the principle of our invention and have described what we now consider to represent its best em- 10 'bodiments. However, we desire to have it understood that the invention may be practiced otherwise than as specifically described.

We claim as our invention:

1. A method for improving a magnetic property of a magnetic aluminum-iron alloy, with comprises heating sheets of a thickness not exceeding 25 mils of a magnetic alloy consisting essentially of at least 14 Weight percent and not exceeding 17.5 percent of aluminum, from a small but significant amount up to 0.5% of at least one element for improving the rollability of the alloy selected from the group consisting of zirconium and boron, the amount thereof being sufiicient to raise the recrystallization temperature of the alloy, and the remainder iron, in a protective atmosphere at a temperature of from 1150 C. to 1300 C. for about 15 minutes to 5 hours, cooling the annealed alloy to about 550 to 750 C. and then quenching the alloy to about room temperature.

2. A method according to claim 1 in which said alloy is heated in dry hydrogen at a temperature of at least about 1200 C., and the resulting annealed material is water quenched.

3. A method of improving the magnetic properties of coercive force and maximum permeability of a magnetic aluminum-iron alloy, which comprises heating a magnetic alloy consisting essentially of 15.2 to 17.5 weight percent of aluminum, from a small but significant amount up to 0.5% zirconium, the amount thereof being sufiicient to raise the recrystallization temperature of the alloy, up to 0.5% boron, and the remainder iron, in dry hydrogen at a temperature of from 1150" to 1300" C. for about /2 to 5 hours, cooling the annealed alloy to about 550 to 750 C. and then quenching the alloy to about room temperature.

4. A method according to claim 3 in which said alloy is in the form of a tape of about 3 to 25 mils in thickness, said annealing temperature is about 1200" C., and the annealed tape is water quenched.

5. A method of reducing a brittle magnetic alloy plate, consisting essentially of 14 to 17.5 weight percent of aluminum and the remainder iron, to a thin tape of less than about 25 mils in thickness which comprises hot rolling such an alloy at a temperature above the recrystallization temperature thereof a plurality of passes and controlling the reduction per pass to 10 to 15 percent of the thickness of the material at the beginning of each pass.

6. In the production of a tape of a brittle magnetic aluminum-iron alloy containing at least about 14 weight percent of aluminum, in which the alloy is warm rolled at a temperature approaching the recrystallization temperature for the alloy, the improvement which comprises raising the recrystallization temperature of the alloy by including therein a small but effective amount of zirconium sufiicient to raise the recrystallization temperature thereof, and then rolling the resulting alloy at a temperature approaching the resulting higher recrystallization temperature to take advantage of increased ductility at said higher temperature.

References Cited in the file of this patent UNITED STATES PATENTS Nachm an Aug. 6, 1957 OTHER REFERENCES 

5. A METHOD OF REDUCING A BRITTLE MAGNETIC ALLOY PLATE, CONSISTING ESSENTIALLY OF 14 TO 17.5 WEIGHT PERCENT OF ALUMINUM AND THE REMAINDER IRON, TO A THIN TAPE OF LESS THAN ABOUT 25 MILS IN THICKNESS WHICH COMPRISES HOT ROLLING SUCH AN ALLOY AT A TEMPERATURE ABOVE THE RECRYSTALLIZATION TEMPERATURE THEREOF A PLURALITY OF PASSES AND CONTROLLING THE REDUCTION PER PASS TO 10 TO 15 PERCENT OF THE THICKNESS OF THE MATERIAL AT THE BEGINNING OF EACH PASS. 